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is a truism that since the appearance of the Origin of Species the application of the evolutionary hypothesis to the interpretation and illumination of the problems of human thought and conduct has been widened until now no field of inquiry escapes its influence. And it is not too much to say that the greater part of the scientific work of the last half century has been done under the stimulus of Darwin and of the conceptions and methods which he developed and illustrated. Modern science is concerned primarily with the historical and genetic aspects of phenomena, with their origin and the order of their development. The astronomer, e. g., asks how a solar system originates, and what are the forces operative in its development; the biologist wishes to know the primitive organisms from which spring the more highly developed forms of plant and animal life; the historian and sociologist study the life and institutions of primitive peoples in search of the origin of the customs and usages which are fundamental in social groups.